runtime: [System.Memory] Embedded Reference Types compiler bug

Code that was previously working (on 4.5.0-preview2-25707-02 , which seems to have disappeared!?) breaks on the latest preview: 4.5.0-preview1-26002-01, this is breaking deployment of new CI infrastructure as the working package is not obtainable. I have tried to hunt down the the issue, but it is beyond my understanding.

Repro steps

dotnet new console
dotnet add package System.Memory -v 4.5.0-preview1-26002-01 -s https://dotnet.myget.org/F/aspnetcore-dev/api/v3/index.json
Edit Program.cs and insert ReadOnlySpan<char> x = "hello".AsReadOnlySpan(); before the print statement
Run dotnet build

Project file (repo.csproj)

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="System.Memory" Version="4.5.0-preview1-26002-01" />
  </ItemGroup>
</Project>

Source file (Program.cs)

using System;

namespace repo
{
    class Program
    {
        static void Main(string[] args)
        {
            ReadOnlySpan<char> x = "hello".AsReadOnlySpan();
            Console.WriteLine("Hello World!");
        }
    }
}

Expected behavior

Expected that the above code works, the usage was taken from the Span doco (https://github.com/dotnet/corefxlab/blob/master/docs/specs/span.md)

Actual behavior

Compiler error: Program.cs(10,12): error CS0619: ‘ReadOnlySpan<char>’ is obsolete: ‘Types with embedded references are not supported in this version of your compiler.’ [/tmp/repo/repo.csproj]

Known workarounds

If you have a cached version of 4.5.0-preview2-25707-02 , you can use this and there will be no errors

Related information

Output of dotnet --info

.NET Command Line Tools (2.0.3)

Product Information:
 Version:            2.0.3
 Commit SHA-1 hash:  eb1d5ee318

Runtime Environment:
 OS Name:     debian
 OS Version:  9
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /usr/share/dotnet/sdk/2.0.3/

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.3
  Build    : a9190d4a75f4a982ae4b4fa8d1a24526566c69df

Edit: Tagging area owners @KrzysztofCwalina and @ahsonkhan

About this issue

Original URL
State: closed
Created 7 years ago
Reactions: 1
Comments: 34 (11 by maintainers)

Commits related to this issue

Bump lang version https://github.com/dotnet/corefx/issues/25669 — committed to SixLabors/ImageSharp.Web by JimBobSquarePants 6 years ago

Most upvoted comments

@ahsonkhan I’ve confirmed this is an issue with ReSharper, as suspending it removes the error message - I’ll open a ticket with JetBrains instead!

cocowalla on May 12, 2018

dotnet build works correctly in my case, however, vscode shows the error as a tooltip and in the ‘problems’ pane. I presume its not using the correct roslyn version but i can’t figure out how to change that.

tmitchel2 on Dec 28, 2017

@ahsonkhan I’m ok now, apologies for not getting back to you. Turned out it was a Resharper bug.

JimBobSquarePants on May 12, 2018

I’m on VS 2017 15.7.1 and having this same problem with the latest .NET Core 2.1 RC. Strange thing is, if I set LangVersion to 7.2, it goes away - if it’s latest or 7.3, the error comes back.

cocowalla on May 11, 2018

I’m experiencing the same issue in Visual Studio 15.6.7 with VB 15.5. I have added <LangVersion>Latest</LangVersion> in <PropertyGroup> in my .vbproj file. But this error is still showing. I clearly know that System.Span(Of T) can’t be stored on heap, so I don’t want to see the BC30668 error preventing me from compiling my code. I have to downgrade System.Memory to 4.4.0-preview1-25305-02 to suppress this error.

Nukepayload2 on May 1, 2018

Right, excellent @ahsonkhan thank you for solving this one, which was really a problem on my end. In summary, it previously worked (boxing a Span) due to the compiler being less stringent about the correctness of boxing a stack only type (in other words, my code was working but probably broken!)

ghost on Dec 4, 2017

Hi @ahsonkhan, I am doing so now (sorry slow internet!)

ghost on Dec 4, 2017

This is a bit problematic given that System.Memory is now locked into a specific language and compiler version (which means ill have to remove it as a dependency).

As long as your code isn’t using any of the new language features (like ref readonly/etc) then you don’t need to bump your language version to use System.Memory.

The compiler update is there to ensure correct usage of Span and catch programming errors at compile time instead of the program crashing at runtime.

~What version of the dotnet cli are you using to compile your project?~ Edit: Just noticed the version info in the initial repro. If you use the latest preview cli, your app should compile fine as well without having to explicitly install the compiler package.

You can see the version if you run the dotnet --info command

Essentially, with the latest cli, I cannot repro the issue using your initial steps. Let me know if that works for you.

Is there any option for having a System.Memory that works with netstandard?

System.Memory should already work with netstandard. We have netstandard libraries today in corefxlab that reference System.Memory and work. Example: https://github.com/dotnet/corefxlab/blob/master/src/System.Buffers.Primitives/System.Buffers.Primitives.csproj#L12

Does this prevent F# from using System.Memory now?

I don’t see any reason why it would. It should still work as expected. Please let me know if you are observing any issues.

open System

[<EntryPoint>]
open System

[<EntryPoint>]
let main argv =
    let array1 = [| 1; 2; 3 |]
    let span = new Span<int>(array1)
    printfn "I am using Span of length %i" span.Length // I am using Span of length 3
    0

ahsonkhan on Dec 4, 2017